diff --git a/ext/misc/appendvfs.c b/ext/misc/appendvfs.c
index ba6cc2c0b8..eb9ed01f62 100644
--- a/ext/misc/appendvfs.c
+++ b/ext/misc/appendvfs.c
@@ -657,6 +657,7 @@ int sqlite3_appendvfs_init(
   (void)pzErrMsg;
   (void)db;
   pOrig = sqlite3_vfs_find(0);
+  if( pOrig==0 ) return SQLITE_ERROR;
   apnd_vfs.iVersion = pOrig->iVersion;
   apnd_vfs.pAppData = pOrig;
   apnd_vfs.szOsFile = pOrig->szOsFile + sizeof(ApndFile);
diff --git a/ext/misc/cksumvfs.c b/ext/misc/cksumvfs.c
index 6994dc7760..8c340889fe 100644
--- a/ext/misc/cksumvfs.c
+++ b/ext/misc/cksumvfs.c
@@ -823,6 +823,7 @@ static int cksmRegisterVfs(void){
   sqlite3_vfs *pOrig;
   if( sqlite3_vfs_find("cksmvfs")!=0 ) return SQLITE_OK;
   pOrig = sqlite3_vfs_find(0);
+  if( pOrig==0 ) return SQLITE_ERROR;
   cksm_vfs.iVersion = pOrig->iVersion;
   cksm_vfs.pAppData = pOrig;
   cksm_vfs.szOsFile = pOrig->szOsFile + sizeof(CksmFile);
@@ -870,9 +871,6 @@ int sqlite3_cksumvfs_init(
   SQLITE_EXTENSION_INIT2(pApi);
   (void)pzErrMsg; /* not used */
   rc = cksmRegisterFunc(db, 0, 0);
-  if( rc==SQLITE_OK ){
-    
-  }
   if( rc==SQLITE_OK ){
     rc = cksmRegisterVfs();
   }
diff --git a/ext/misc/memvfs.c b/ext/misc/memvfs.c
index 27a61c35e4..83fc9468e6 100644
--- a/ext/misc/memvfs.c
+++ b/ext/misc/memvfs.c
@@ -559,6 +559,7 @@ int sqlite3_memvfs_init(
   int rc = SQLITE_OK;
   SQLITE_EXTENSION_INIT2(pApi);
   mem_vfs.pAppData = sqlite3_vfs_find(0);
+  if( mem_vfs.pAppData==0 ) return SQLITE_ERROR;
   mem_vfs.szOsFile = sizeof(MemFile);
   rc = sqlite3_vfs_register(&mem_vfs, 1);
 #ifdef MEMVFS_TEST
diff --git a/ext/misc/vfslog.c b/ext/misc/vfslog.c
index 24a46a921f..cb5bc5513a 100644
--- a/ext/misc/vfslog.c
+++ b/ext/misc/vfslog.c
@@ -754,6 +754,7 @@ static int vlogCurrentTimeInt64(sqlite3_vfs *pVfs, sqlite3_int64 *p){
 */
 int sqlite3_register_vfslog(const char *zArg){
   vlog_vfs.pVfs = sqlite3_vfs_find(0);
+  if( vlog_vfs.pVfs==0 ) return SQLITE_ERROR;
   vlog_vfs.base.szOsFile = sizeof(VLogFile) + vlog_vfs.pVfs->szOsFile;
   return sqlite3_vfs_register(&vlog_vfs.base, 1);
 }
diff --git a/ext/misc/vfsstat.c b/ext/misc/vfsstat.c
index 186ed788fc..83a7a3df75 100644
--- a/ext/misc/vfsstat.c
+++ b/ext/misc/vfsstat.c
@@ -806,6 +806,7 @@ int sqlite3_vfsstat_init(
   int rc = SQLITE_OK;
   SQLITE_EXTENSION_INIT2(pApi);
   vstat_vfs.pVfs = sqlite3_vfs_find(0);
+  if( vstat_vfs.pVfs==0 ) return SQLITE_ERROR;
   vstat_vfs.base.szOsFile = sizeof(VStatFile) + vstat_vfs.pVfs->szOsFile;
   rc = sqlite3_vfs_register(&vstat_vfs.base, 1);
   if( rc==SQLITE_OK ){
diff --git a/ext/misc/zipfile.c b/ext/misc/zipfile.c
index 86f7ba0f94..b727f9f2be 100644
--- a/ext/misc/zipfile.c
+++ b/ext/misc/zipfile.c
@@ -1486,6 +1486,7 @@ static int zipfileBegin(sqlite3_vtab *pVtab){
 static u32 zipfileTime(void){
   sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
   u32 ret;
+  if( pVfs==0 ) return 0;
   if( pVfs->iVersion>=2 && pVfs->xCurrentTimeInt64 ){
     i64 ms;
     pVfs->xCurrentTimeInt64(pVfs, &ms);
diff --git a/ext/rbu/rbu.c b/ext/rbu/rbu.c
index 91773409cf..7a24db214e 100644
--- a/ext/rbu/rbu.c
+++ b/ext/rbu/rbu.c
@@ -56,7 +56,7 @@ void usage(const char *zArgv0){
 
 void report_default_vfs(){
   sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
-  fprintf(stdout, "default vfs is \"%s\"\n", pVfs->zName);
+  fprintf(stdout, "default vfs is \"%s\"\n", pVfs ? pVfs->zName : "NULL");
 }
 
 void report_rbu_vfs(sqlite3rbu *pRbu){
diff --git a/manifest b/manifest
index a82bb9f97a..6c3479e0b1 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Prevent\san\sinfinite\sloop\sin\sthe\strim()\sSQL\sfunction\sif\sthe\ssecond\sargument\nis\sa\scarefully\smalformed\sUTF8\sstring.
-D 2021-06-15T14:34:21.347
+C Add\sNULL\schecks\son\sall\ssqlite3_vfs_find(0)\scalls.\s\sThis\sis\snot\sstrictly\nnecessary.\s\sThere\sare\sno\svulnerabilities\shere.\s\sHowever,\sadding\sthese\nchecks\savoids\sunnecessary\sstatic\sanalyzer\scomplaints.\n[forum:/forumpost/ce1193be15|Forum\spost\sce1193be15].
+D 2021-06-15T15:15:40.609
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -286,12 +286,12 @@ F ext/lsm1/tool/mklsm1c.tcl f31561bbee5349f0a554d1ad7236ac1991fc09176626f529f607
 F ext/misc/README.md d6dd0fe1d8af77040216798a6a2b0c46c73054d2f0ea544fbbcdccf6f238c240
 F ext/misc/amatch.c e3ad5532799cee9a97647f483f67f43b38796b84b5a8c60594fe782a4338f358
 F ext/misc/anycollseq.c 5ffdfde9829eeac52219136ad6aa7cd9a4edb3b15f4f2532de52f4a22525eddb
-F ext/misc/appendvfs.c 500fef0736caafc629ca1dbae348a121367eaa4ed8c385c291cb9ad65ea790fb
+F ext/misc/appendvfs.c 9642c7a194a2a25dca7ad3e36af24a0a46d7702168c4ad7e59c9f9b0e16a3824
 F ext/misc/blobio.c a867c4c4617f6ec223a307ebfe0eabb45e0992f74dd47722b96f3e631c0edb2a
 F ext/misc/btreeinfo.c d28ce349b40054eaa9473e835837bad7a71deec33ba13e39f963d50933bfa0f9
 F ext/misc/carray.c b75a0f207391038bf1540d3372f482a95c3613511c7c474db51ede1196321c7c
 F ext/misc/carray.h de74ac70b2338f416723f7d538026e8ec0b7f1d388319f8f140c9a4d7677f02e
-F ext/misc/cksumvfs.c 2c6b07714f3be6c1200671c53aa781a86d2c472c0fcb2fff520375362eb94303
+F ext/misc/cksumvfs.c b42ef52eaaa510d54ec320c87bea149e934a3b06cd232be2093562bf669bd572
 F ext/misc/closure.c dbfd8543b2a017ae6b1a5843986b22ddf99ff126ec9634a2f4047cd14c85c243
 F ext/misc/completion.c 6dafd7f4348eecc7be9e920d4b419d1fb2af75d938cd9c59a20cfe8beb2f22b9
 F ext/misc/compress.c 3354c77a7c8e86e07d849916000cdac451ed96500bfb5bd83b20eb61eee012c9
@@ -308,7 +308,7 @@ F ext/misc/ieee754.c cd6ab89f85fda8a020559b3f4d03001a8a62dd856beda5af3f558621d12
 F ext/misc/json1.c 76c5d9e0960fd15b4be79dacb76d872b4d0d983ce13e72ebfe9481d82cb9345d
 F ext/misc/memstat.c 3017a0832c645c0f8c773435620d663855f04690172316bd127270d1a7523d4d
 F ext/misc/memtrace.c 7c0d115d2ef716ad0ba632c91e05bd119cb16c1aedf3bec9f06196ead2d5537b
-F ext/misc/memvfs.c ab36f49e02ebcdf85a1e08dc4d8599ea8f343e073ac9e0bca18a98b7e1ec9567
+F ext/misc/memvfs.c 7dffa8cc89c7f2d73da4bd4ccea1bcbd2bd283e3bb4cea398df7c372a197291b
 F ext/misc/mmapwarm.c 347caa99915fb254e8949ec131667b7fae99e2a9ce91bd468efb6dc372d9b7a9
 F ext/misc/nextchar.c 7877914c2a80c2f181dd04c3dbef550dfb54c93495dc03da2403b5dd58f34edd
 F ext/misc/noop.c 81efe4cad9ec740e64388b14281cb983e6e2c223fed43eb77ab3e34946e0c1ab
@@ -332,14 +332,14 @@ F ext/misc/uint.c 053fed3bce2e89583afcd4bf804d75d659879bbcedac74d0fa9ed548839a03
 F ext/misc/unionvtab.c 36237f0607ca954ac13a4a0e2d2ac40c33bc6e032a5f55f431713061ef1625f9
 F ext/misc/urifuncs.c f71360d14fa9e7626b563f1f781c6148109462741c5235ac63ae0f8917b9c751
 F ext/misc/uuid.c 5bb2264c1b64d163efa46509544fd7500cb8769cb7c16dd52052da8d961505cf
-F ext/misc/vfslog.c 3b25c2f56ba60788db247287be6ab024b53c4afffd412b4876db563389be0d35
-F ext/misc/vfsstat.c 389ea13983d3af926504c314f06a83cc858d5adc24b40af74aaed1fece00c118
+F ext/misc/vfslog.c 3932ab932eeb2601dbc4447cb14d445aaa9fbe43b863ef5f014401c3420afd20
+F ext/misc/vfsstat.c 474d08efc697b8eba300082cb1eb74a5f0f3df31ed257db1cb07e72ab0e53dfb
 F ext/misc/vtablog.c 5538acd0c8ddaae372331bee11608d76973436b77d6a91e8635cfc9432fba5ae
 F ext/misc/vtshim.c 1976e6dd68dd0d64508c91a6dfab8e75f8aaf6cd
 F ext/misc/wholenumber.c a838d1bea913c514ff316c69695efbb49ea3b8cb37d22afc57f73b6b010b4546
-F ext/misc/zipfile.c acbad31bd9c9ec3540fa72b2e3fcd6f757eb33117d51528c0e13d0da5c836908
+F ext/misc/zipfile.c b7261ef6dbc2d18924ff80c40fb5d56c9ccfee3f822a7d3d43b7c87af3d27218
 F ext/misc/zorder.c b0ff58fa643afa1d846786d51ea8d5c4b6b35aa0254ab5a82617db92f3adda64
-F ext/rbu/rbu.c b880ca5cb857d6d6f52e72eb7397813058ef48c78c5402cd04ff2b6b5437f622
+F ext/rbu/rbu.c 801450b24eaf14440d8fd20385aacc751d5c9d6123398df41b1b5aa804bf4ce8
 F ext/rbu/rbu1.test c62904bd9526dcdc3496a21199aaf14ae191bbadbf67f076bf16be6b3f2115c2
 F ext/rbu/rbu10.test 0a201c32202143f23c81c0144503da339786fc20acb7a2fda11601b65659f314
 F ext/rbu/rbu11.test 5c834cf491086b45e071eabf71f708febc143e86a384a92de69e0b1a4cace144
@@ -515,7 +515,7 @@ F src/mem1.c c12a42539b1ba105e3707d0e628ad70e611040d8f5e38cf942cee30c867083de
 F src/mem2.c b93b8762ab999a29ae7751532dadf0a1ac78040308a5fb1d17fcc365171d67eb
 F src/mem3.c 30301196cace2a085cbedee1326a49f4b26deff0af68774ca82c1f7c06fda4f6
 F src/mem5.c 9bf955937b07f8c32541c8a9991f33ce3173d944
-F src/memdb.c f6ce717b26cd51a24cda62fce611b4b72b3db367113374aa498e489a69470715
+F src/memdb.c 2f2e8efc6e531c59cf8255f0bf4ad81f2e88e0a394581244154c8cf5141757ce
 F src/memjournal.c a85f0dc5c02a42453d0bc3819ecfb5666cb6433e5deefcd93ccbe05c9f088b83
 F src/msvc.h 3a15918220367a8876be3fa4f2abe423a861491e84b864fb2b7426bf022a28f8
 F src/mutex.c 5e3409715552348732e97b9194abe92fdfcd934cfb681df4ba0ab87ac6c18d25
@@ -541,11 +541,11 @@ F src/pragma.c eb42cb9bec189cf18cef5d8fcae56e13bb73ef2b019b198fb48740ced81bce95
 F src/pragma.h 8dc78ab7e9ec6ce3ded8332810a2066f1ef6267e2e03cd7356ee00276125c6cf
 F src/prepare.c 0d53d20532aada295c1690792a125adbd6435f5ce703ff0adf1b9b3605238b67
 F src/printf.c 78fabb49b9ac9a12dd1c89d744abdc9b67fd3205e62967e158f78b965a29ec4b
-F src/random.c 80f5d666f23feb3e6665a6ce04c7197212a88384
+F src/random.c 097dc8b31b8fba5a9aca1697aeb9fd82078ec91be734c16bffda620ced7ab83c
 F src/resolve.c 35630effd4d16d2373caa41bae40a3d71f853f3ad0cb4f572f2ed4b8c350c1e9
 F src/rowset.c ba9515a922af32abe1f7d39406b9d35730ed65efab9443dc5702693b60854c92
 F src/select.c 4fa607bab6bcc580f12dbaf9c800b2250a1e408f10321a1d3bcb1dd30c447e62
-F src/shell.c.in 586493be0d3a2fc1e6803577d683697dfefc0fb305cc966bb389ce4045cbc19d
+F src/shell.c.in f3e91c697f33daae14923355dcadfc26bb0c1eabdb343e5508706893e017a0a6
 F src/sqlite.h.in f450394634eac00bc680c0e91582b818359c6ad61149f49f90fb6ecbd526b51f
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 61b38c073d5e1e96a3d45271b257aef27d0d13da2bea5347692ae579475cd95e
@@ -623,7 +623,7 @@ F src/vdbeapi.c aa5aaf2c37676b83af5724c6cd8207a3064ed46a217fd180957f75ac84f7a2a5
 F src/vdbeaux.c 065a10392378109f08435bd50d03dff315e384cde2831d6b8dbaec05f33b10af
 F src/vdbeblob.c c6b8db50b227f66fb404215732068df76485b5b433e5f9d4d9ac27410b218193
 F src/vdbemem.c 53881aa0a7845922a075b3f375695588618098871a7a4120af4c297b80fa3e64
-F src/vdbesort.c f5b5e473a7cee44e47a94817b042fd7172cf3aa2c0a7928a8339d612bcfdec5a
+F src/vdbesort.c cd5130f683706c1a43e165a74187745fb3351cb56052cf9dc91de820634bbde2
 F src/vdbetrace.c 666c6fd9f1b62be6999e072a45b913e3c2c3518bc60dfd4d54fe304130acb724
 F src/vdbevtab.c f99b275366c5fc5e2d99f734729880994ab9500bdafde7fae3b02d562b9d323c
 F src/vtab.c b928405ccb66040fc6c3a11eaa93ddb02cbf20f9ab6860b301b222b9b50dc089
@@ -1918,7 +1918,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d4d9869c30710914b7ba51221b2c2223a9cf16b913bd6f3866ae747494a116af
-R 1140229a8b312b5b0ad935a5a74919ba
+P 829343c26ed7b87fafc70de3369625209bad91e79bb7ca2946d5c8d61cc1c3c4
+R 9aa6f2e0346815fa6d5daf16e2359ae5
 U drh
-Z dd9b2df17b0c7422257831b53e0c4377
+Z 993cbec21430496a6c026bc47f824357
diff --git a/manifest.uuid b/manifest.uuid
index 1079eb364d..2fbcda8cbf 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-829343c26ed7b87fafc70de3369625209bad91e79bb7ca2946d5c8d61cc1c3c4
\ No newline at end of file
+272a15b9f418fb0b31a9808f7c42c20cf52318035ff98935d8e8519634357e8d
\ No newline at end of file
diff --git a/src/memdb.c b/src/memdb.c
index 965ec36d41..4e5751f931 100644
--- a/src/memdb.c
+++ b/src/memdb.c
@@ -861,7 +861,9 @@ end_deserialize:
 */
 int sqlite3MemdbInit(void){
   sqlite3_vfs *pLower = sqlite3_vfs_find(0);
-  unsigned int sz = pLower->szOsFile;
+  unsigned int sz;
+  if( NEVER(pLower==0) ) return SQLITE_ERROR;
+  sz = pLower->szOsFile;
   memdb_vfs.pAppData = pLower;
   /* The following conditional can only be true when compiled for
   ** Windows x86 and SQLITE_MAX_MMAP_SIZE=0.  We always leave
diff --git a/src/random.c b/src/random.c
index d4ae77c435..87f9e2cecb 100644
--- a/src/random.c
+++ b/src/random.c
@@ -76,11 +76,16 @@ void sqlite3_randomness(int N, void *pBuf){
   ** number generator) not as an encryption device.
   */
   if( !wsdPrng.isInit ){
+    sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
     int i;
     char k[256];
     wsdPrng.j = 0;
     wsdPrng.i = 0;
-    sqlite3OsRandomness(sqlite3_vfs_find(0), 256, k);
+    if( NEVER(pVfs==0) ){
+      memset(k, 0, sizeof(k));
+    }else{
+      sqlite3OsRandomness(pVfs, 256, k);
+    }
     for(i=0; i<256; i++){
       wsdPrng.s[i] = (u8)i;
     }
diff --git a/src/shell.c.in b/src/shell.c.in
index 5aa28d0b6a..0f8de61a14 100644
--- a/src/shell.c.in
+++ b/src/shell.c.in
@@ -226,6 +226,7 @@ static sqlite3_int64 timeOfDay(void){
   static sqlite3_vfs *clockVfs = 0;
   sqlite3_int64 t;
   if( clockVfs==0 ) clockVfs = sqlite3_vfs_find(0);
+  if( clockVfs==0 ) return 0;  /* Never actually happens */
   if( clockVfs->iVersion>=2 && clockVfs->xCurrentTimeInt64!=0 ){
     clockVfs->xCurrentTimeInt64(clockVfs, &t);
   }else{
diff --git a/src/vdbesort.c b/src/vdbesort.c
index f61b8b7320..397935aa8c 100644
--- a/src/vdbesort.c
+++ b/src/vdbesort.c
@@ -1073,8 +1073,9 @@ static void vdbeSorterWorkDebug(SortSubtask *pTask, const char *zEvent){
   fprintf(stderr, "%lld:%d %s\n", t, iTask, zEvent);
 }
 static void vdbeSorterRewindDebug(const char *zEvent){
-  i64 t;
-  sqlite3OsCurrentTimeInt64(sqlite3_vfs_find(0), &t);
+  i64 t = 0;
+  sqlite3_vfs *pVfs = sqlite3_vfs_find(0);
+  if( ALWAYS(pVfs) ) sqlite3OsCurrentTimeInt64(pVfs, &t);
   fprintf(stderr, "%lld:X %s\n", t, zEvent);
 }
 static void vdbeSorterPopulateDebug(